Mold inspection and testing in Tyler Run, PA

Tyler Run is small — a couple of thousand people on the hills south of the city, usually spoken about together with Queens Gate next door. The housing goes back to around the 1940s in places, with later building filling in around it, so you'll find a wartime-era house and a 1980s one on the same street. But the age of the house matters less here than almost anywhere else I work, because the dominant variable is the topography.

Building into a hillside gives you the walkout basement, which is a genuinely different structure from a full basement or a crawl space. One or two walls are buried in the grade. Another is above ground with doors and windows in it. The buried walls are in permanent contact with soil that sits in the fifties year round, so they run cool; the daylight wall is exposed to outside air and sun. Inside a single finished room you have a cool damp end and a warm dry end, and the corner where they meet is where humid air condenses out on the coldest surface it can find. When a walkout basement grows mold behind the drywall, that corner is where it starts nine times out of ten. Everybody looks at the walkout doors, where there's plenty of light to see by. The problem is at the other end.

Then there's water on the surface. Storm water on a slope is not a local matter. The rain that falls on the properties above you, on the streets above those, and on every driveway and roof between here and the top of the hill has to travel downhill, and a good deal of it crosses your lot on the way to the drainage swales and to Tyler Run itself. If the grade immediately around your foundation has flattened, if a walk or patio has settled toward the house, or if a swale that used to carry water around the building has been filled in for a lawn, that runoff loads the foundation wall directly. The creek does its part too — small watersheds like this rise fast in a hard rain and drop just as fast, which is enough to wet the low corner of a lot and anything stored in the basement there.

Retaining walls deserve their own paragraph. Half the yards here have one, and many of them are older than the idea that a retaining wall needs a drainage layer and a weep path behind it. When that drainage fails or was never there, the wall holds saturated soil against whatever is behind it — sometimes the house itself. On the inside you get an even band of elevated moisture along the bottom of the wall for its whole length, which is a distinctive pattern: plumbing leaks are localized, hydraulic loading is not.

Above grade, decks and patios built over the walkout are a recurring source. The ledger board, the door threshold and the flashing where the deck meets the house are all places water gets in and runs along the rim joist. Inside, that shows up as a wet header above the walkout doors and mold on the back of the trim, well away from anything you'd associate with the deck.

With rentals — including student housing associated with York College a short distance away — the same physics apply, just with faster turnover and more cosmetic repair layered over it. Whoever hires me, the inspection covers the lot and the structure, and the report says what the readings say.